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The use of a novel type of electroactive ion-partitioning membrane is employed for the development of a potassium selective chemically modified field-effect transistor (CHEMFET). As is in the case of optodes, the membrane is doped with two ion carriers, one selective to the ion of interest (K+) and the other to protons. The careful optimization of the chemical composition of the membrane allows for ion-exchange to take place between the partitioned cation and the membrane protons. The potassium ions extracted into the bulk of the membrane phase displace protons of equal charge out of the membrane, and towards the sample solution and the pH-sensitive transducer. The potentiometric response of the sensor is based on the magnitude of this proton flux, as it is measured by the pH-ISFET. Both the effect of the ionic composition of the sample solution and the chemical constituents of the polymeric membrane are evaluated in relation to the potentiometric response of the CHEMFET. It is shown that the increase of the mole ratios of potassium to proton in the sample solution, the use of small amounts of a highly acidic proton carrier, and the use of a low dielectric constant plasticizer of the sensor to potassium ions. The performance of the K-CHEMFET developed based on the optimized ion-partitioning membrane is evaluated by the measurement of potassium levels in real blood serum samples. |
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